The invention is directed to a double seat valve with means for preventing leakage, particularly for the food and beverage industry, which has in its housing two valve disks (6, 7) that cooperate with one another and define a leakage space (10) which customarily opens out into the open via lines (11). A shared drive unit is provided for the actuation of the two valve disks (6, 7). This drive unit contains a cylinder (17) with a first work piston (18) which is loaded at both sides by pressure springs (29, 22) and is fixedly connected with the valve stem or valve shaft (13) of the lower valve disk (7), this valve disk (13) penetrating the upper valve disk (6) and its tubular shaft (14) in a telescoping manner, the shaft, in turn, projecting into the cylinder (17) by its upper end and having an abutment (31) at that location for the lower pressure spring (29) which presses the upper valve disk (6) into its seat (8), and a second work piston (36) which acts on the tubular shaft and is movable on the tubular shaft is arranged under the first work piston (18) in the cylinder (17), and a third work piston (30) which acts on the lower valve disk is arranged above the first work piston.
A blocking valve of the type described above is known from DE-A1 30 05 329.
The seat faces of the two valve disks are constructed so as to be conical and are aligned in such a way that the two valve disks move into the seat face in the same direction. A leakage space which customarily discharges into the open via a line is formed between the valve disks.
Further, DE 42 36 464 A1 discloses a double seat valve in which the lower valve disk continues downward into a balance piston which has approximately the same diameter as the lower valve disk in order to prevent the lower valve disk from lifting due to pressure shocks and to prevent medium from entering the leakage space. Pressure shocks in the pipeline accordingly act on the balance cylinder and valve disk with the same force, so that the pressure forces are balanced in the axial direction.
The known valves can carry out three functions. To open the valve, both valve disks are lifted; to clean the valve seats, the lower or upper valve disk can each be individually moved out of its seat face slightly in order to clean the seat face.
For this purpose, drive units are provided for the valves, these drive units having cylinders which are arranged in series and in which the required pistons are arranged. The pistons act on the two valve disks via two concentric valve shafts.
For opening, a first work piston which is connected with the lower valve disk via a valve shaft is acted upon by compressed air. Accordingly, the first piston is moved upward against the force of a first spring while carrying along the lower valve disk, this spring being further pretensioned until the lower valve disk abuts against the upper valve disk. The leakage space is then closed. When lifted further, the two valve disks move jointly upward, so that the valve is opened.
In the opened state, a second spring which is supported against stops at the valve shaft and at the tubular valve shaft press the two valve disks together.
The closing of the valve proceeds in the reverse order; but the first work piston is moved by the force of the first spring in the pressureless state. As soon as the upper valve disk has reached its seat, the two valve disks separate and the lower valve disk moves into its seat. In so doing, the second spring is further compressed.
To clean the valve seats, the valve disks must be lifted individually. A second and a third piston are provided for this purpose. These pistons act individually, via the valve shafts, on the lower and upper valve disks, respectively.
The second piston for the cleaning lift of the lower valve disk is located in its own cylinder above the cylinder for the first piston. The valve shaft for the lower valve disk is guided in this second cylinder. As soon as its underside is acted upon by compressed air, it lifts the associated valve shaft via a suitable stop and, along with the valve shaft, lifts the lower valve disk out of its seat. A suitable cleaning medium can penetrate into the leakage chamber through an annular gap formed in this way between the valve disk and valve seat.
To clean the upper valve seat, the third piston which is arranged in the cylinder between the first piston and the lower housing wall, is acted upon from below by compressed air. The piston is lifted until it abuts against an abutment arranged at the tubular valve shaft. The upper valve disk is accordingly also lifted from its seat somewhat via the valve shaft. The associated valve seat is rinsed by the penetrating cleaning medium.
The construction of the drive unit turns out to be quite costly due to the large number of switching functions.